The present invention is related to gain controlled common-emitter amplifiers and more specifically to a common-emitter amplifier having a controllable dynamic voltage gain. The circuit is particularly adaptable to hybrid circuits and facilitates the fabrication of such circuits without excessive trimming of resistors and/or matching of active components.
Previously designed amplifier circuits have been fabricated using field effect transistors (FET) as the gain controlling components, but the operating characteristics of the FET's vary substantially from lot to lot and even within a graded lot, thereby increasing the difficulty of fabrication of the hybrid devices. Specifically, it was necessary to "hot trim" the resistors associated with each FET to match the circuit gains and operating points, which required additional time and expense.
The present invention, however, simplifies the fabrication of such circuits due to the uniformity of bipolar transistors and the ability to "cold trim" components to fixed design values.